The production of copper typically involves a multi-step procedure which includes concentration, smelting, converting, refining, anode casting and electrolytic refining procedures. Typically, starting with an ore comprising one or more of a copper sulfide or copper-iron-sulfide mineral, such as chalcocite, chalcopyrite and bornite, the ore is converted to a concentrate containing usually between 25 and 35 weight percent copper. The concentrate is then converted with heat and oxygen first to a matte and then to blister copper. The further refining of the blister copper in an anode furnace accomplishes the further reduction of oxygen and sulfur impurities in the blister copper, typically from levels as high as 0.80% and 1.0%, respectively, to levels as low as 0.05% and 0.002%, respectively and is usually carried out in the temperature range of about 1090° C. (2000° F.) to 1300° C. (2400° F.). However, during the anode refining process, solid accretions accumulate in the anode furnace which tends to adversely affect furnace capacity and ultimately copper production.
Furnace accretions are pervasive in both ferrous and non-ferrous pyrometallurgical reactors. Furnace accretions include hearth accretions and wall (or duct) accretions as well as waste heat boiler throat accretions and uptake shaft accretions observed in flash furnaces. Hearth accretions in non-ferrous reactors have been documented in early converter operations and more recently non-ferrous flash furnaces. The mechanism of hearth accretion formation is thought to be a complex phenomenon that includes factors like slag chemistry, oxygen potential, as well as heat and mass transfer mechanisms. Build-up of hearth accretion appears to be related, at least partially, to efforts to extend campaign life of furnaces and selected furnace operational considerations including slag skimming frequency, porous gas injection mixing plug performance and occasional upstream upset conditions.
An example of the adverse effects of hearth accretions was observed at the smelting operations at Kennecott Utah Copper. As a result of the decreasing furnace capacity from normal operating capacity of about 600 tons to a reduced operating capacity of about 400 tons, the copper anode furnaces used at Kennecott Utah Copper were becoming full after only two blister taps from the flash converter and this shorter furnace fill time reduced the time available for scrap melting. Also, the decreased furnace capacity increased the number of refining cycles to meet the desired output of copper production. In all, the smelter anode productivity at the Kennecott facility had been reduced by up to about 20% due to hearth accretions.
Prior efforts to remove the hearth accretion buildup centered on fluxing and using solid fuels to help melt the buildup. For example, ferrosilicon has been used as a fuel in attempts to melt the hearth accretion buildup. In basic oxygen steelmaking furnaces hearth accretions are typically removed by charging the furnace with ferrosilicon and burning the ferrosilicon with oxygen supplied through the main oxygen lance. An alternative effort to mitigate or remove the hearth accretion buildup in the furnace is soda ash fluxing, with or without addition of lime and aluminum chips (i.e. thermite reaction). However, the disadvantages associated with fuels such as ferrosilicon and soda ash fluxing, including temperature control and localized heat generation may have adverse effects on the campaign life of the anode furnaces. In particular, because the anode furnace geometry is typically not symmetrical with respect to the oxygen source, there are concerns over temperature control and potential for refractory damage by excess localized heat generation when using fuels such as ferrosilicon and soda ash fluxing.
Another technique to remove the hearth accretion buildup that has previously been used is the addition of significant oxy-fuel burner energy in the vicinity of the accretion buildup to partially melt and loosen the accretion. While this solution has proven effective, there are serious concerns regarding the effects of the oxy-fuel burner on refractory integrity as well as environmental concerns associated with increased emissions associated with the oxy-fuel burner.
Traditional coherent jet technology has also been suggested to address the problem of hearth accretions. One such coherent jet system is Praxair's CoJet® system which provides both chemical energy and gas injection capabilities for metallurgical processes such as copper anode refining process. Briefly, the coherent jet process creates a flame shroud around a high velocity gas jet. The flame shroud reduces ambient gas entrainment into the high velocity jet thereby maintaining the jet's velocity profile over longer distances, compared to an un-shrouded gas jet. The coherent jet technology and system has been shown to be potentially useful in copper anode refining as a source of top-blown oxidation and reduction gas jets for fire refining as well as an energy source for increased scrap melting rates. Scrap melting rates of about 9 tonne/h using the traditional coherent jet technology and systems have been demonstrated in one copper anode furnace at Kennecott Utah Copper, with up to 203 tonne scrap melted during one melting period.
However, some operational concerns and disadvantages of using existing or traditional coherent jet systems need to be overcome if use of coherent jet technology for removal of hearth accretions is to become a commercial practicality. These operational concerns include: opening the coherent jet port often required jack-hammering and mag-lancing; connecting the gas supply hoses to the coherent jet lance assembly required elevated work practices and controls; plugging the coherent jet port was difficult and could result in leaks of molten copper; and, the size and weight of the coherent jet lance assembly devices typically required at least two persons to install and remove.
As discussed in more detail in the sections that follow, the presently disclosed system and method for removal of accretions using a simpler coherent jet lance assembly design has overcome many of these difficulties.